Are the general illumination lights out on the backbox panel and on the playfield? The circuit looks super simple. 6.3 volts AC comes directly off the transformer via a green and white wire. It goes directly to a 20 amp fuse. The schematic that I looked at doesn't identify the fuse number. Then the circuit branches off to both J14 and J15 on the power supply board. J14 is for the backbox. Pins 1, 2, and 3 (blue & white wires) are the 6.3 volts AC and pins 7, 8 and 9 (brown wires) are the GI returns. J15 is for the playfield. Pins 2, 3, and 4 (blue & white wires) are the 6.3 volts AC and pins 6, 7, and 8 (brown wires) are the GI returns.